Luminescent material



Patented Sept. 2, 1941 fUNlT-ED STATES PATENT "oi-"Flea LUMINESCENT MATERIAL Gunther Aschermann, Berlin-'Oharlottenburg,

Germany, assignor to General Electricv Company, a corporation oi New York No Drawing. Application September 9, 1940,

German rialNo. 858,115. In

8g- 7 August 10, 1939;

S'Olaims. (01. 250-81) My invention relates to luminescent materials I in general, and more particularly to luminescent silicates ior the production oi light radiations within the short-wave portion, i. e., the blue and long-wave ultra-violet portion, oi the spectrum.

chemically very stable while readily excited by the mercury radiation. However, a disadvantage oi this type oi luminescent material has been that, while it was possible to change the mainly green or yellow-green color oi the emitted light oi these luminescent materials toward the longer wave (yellow to yellow-red) portion oi the spectrum, a considerable displacement oi the wave lengths oi the emitted light toward the shortqwave part oi the spectrum could not be obtained.

One object oi my invention is to provide luminescent silicate materials which will emit blue to ultra-violet radiations when excited to luminescence by the radiations 01' a mercury-vapor discharge. Another obect oi my invention is to provide It has been iou'nd that luminous silicate materials with a very strong blue to ultra-violet radiation can be obtained in a simple manner when, according to the invention, orthosilicates or metasillcates oi aluminum, beryllium or magnesium either by themselves or in mixture, are

activated with cerium sesquioxide (CeaOa). For producing such luminescent materials, very pure silicic acids are mixed with very pure oxides oi aluminum, beryllium or magnesium or mixtures 'thereoi, while cerium-dioxide (CeOa) or cerium salts or cerium-salt solutions are added. The silicic acid and oxides oi aluminum, beryllium or magnesium are in this case used to advantage, in accordance with the iormulas BSiOa-lAhOs (metasilicateL and limos-M120: (orthosilicate) g in a ratio oi 3:1 or 3:2, while the ratio oi the components does not need to correspond to the stoichiometric relations. ilhe quantity oi the added cerium-dioxide or the added cerium salts can fluctuate within wide limits, and may have a value'up to per cent by weight.

Aiter the individual components have been intimately mixed, the mixture is tired at a temperature oi approximately 1100 to l800 0., preierably however at 1250 0.. in a reducing atmosphere. preierably in very pure hydrogen, as a result oi which the added cerium-dioxide or the added cerium salts are converted into ceriumluminescent silicate materials which will emit radiations mainly in the range between 3000 to 4800 angstroms when excited to luminescence by the radiations of a mercury vapor discharge.

The main ieature oi my invention is the use,

oi cerium sesquioxlde (CesOs) to activate the orthosilicates or metasillcates oi aluminum, be

ryllium or magnesium, either by themselves or in mixtures. A iurther ieature oi my invention is the use oi lead or bismuth as a second activator to increase the emission oi such luminous materials. Still another ieature oi my invention is the addition of iiuorides'oi the alkaliearth metals calcium, barium or strontium'to such luminous materials ior the purpose of iacilitating the heating and homogenizing oi the luminous material mixture, and also ior the purpose oi displacing the center oi the light-emission band toward the short-wave side oi the spectrum so as to lie at a value oi approximately 3500 to 3600 angstroms.

Further objects and advantages oi my inven-,

ultra-violet radiation.

sesquioxide. The time oi nring as a rule is about V hour or more; it can. oi course, be shorter at higher temperatures. The resulting compound, which is very much sintered together. is

ground upon cooling and is then immediately ready ior use.

The emission oi the new luminescent materials according to the invention covers mainly the range irom 3000 to 4800 angstroms, although there is still present an emission in the yellow spectral range which, however, is very weak. The center oi the light-emission band oi the luminous,materials with ablue radiation lies at approximately 4000 angstroms. In addition to their application ior changing the light color and ior increasing the light yield oi the mercury discharge, the luminous materials according to the invention can also be utilized where photochemically active rays are desired within the mentioned range. They can consequently be utilized to advantage ior the conversion oi the intensive short-wave line, 2587 angstroms, oi the low-pressure mercury discharge into longer wave It has been iound that, in practice, a luminous eiiect can not be obtained when the cerium is present in the fused luminous material in the quadrivalent oxidation stage.

Thd emission of the new luminous materials can be increased by adding lead or bismuth as the second activator. The lead or the bismuth. in this case, is to be added in the form oi-salts or oxides in a quantity up to 3 per cent of the total mixture.

It is furthermore possible to add to the mixture a fluoride or fluorides oi the alkali-earth metals calcium, barium or strontium; this can be done in quantities up to approximately 50 per cent. By such an admixture not only the sintering or melting, and consequently the homogenizing, oi the luminous material mixture is facilitated, but at thesame time a pronounced displacement oi the light-emission band center toward the'shortwave side of the spectrum is produced by a change in the absorption, so that the center of the band will then lie at a value of approximately 3500 to 3600 angstroms-depending on the additional fluoride that is used. The color of the emitted light in such case is not. blue, but violet. If in addition to such a displacement of the band, an increase in the emission is simultaneously desired, then an admixture of lead orbismuth is to be used in addition to the admixture oi a fluoride. Under certain circumstances, it sufllces to use fluorides which are not chemically pure but to use those which contain a certain quantity of lead or impurities.

A few mixtures suitable for the production of aluminum silicate luminous materials with an admixture of cerium-.sesquioxide, together with their emission range and the intensity the luminous material after it is flred and ground, are given below.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A luminescent substance hi hly responsive to radiation having a wave length oi. 2537 An!- strom units-and highly emissive in the range of approximately 3000 to 4800 Angstrom units, said substance being a silicate of a metal of the group consisting of aluminum, beryllium and magnesium, activated by an addition or up to 30 per cent by weight of cerium sesquioxide.

2. A luminescent substance highly responsive to radiation having a wave length of 2537 Angstrom units and highly emissive in the range of approximately 3000 to 4800 Angstrom units, said substance being a silicate oi a metal of the group consisting of aluminum, beryllium and magneslum, activated by an addition oi cerium sesquioxide and a metal of the group consisting oi lead and bismuth, said metal being added in the form or a suitable compound up to 3 per cent of the total mixture.

3. A luminescent substance highly responsive to radiation having a wave length of 2537 Angstrom units and highly emissive in the range of approximately 3000 to 4800. Angstrom units, said substance being a silicate 0! a metal of the group consisting of aluminum, beryllium and magnesium,.activ ated by an addition 01 cerium 'sesquioxide and a metal of the group consisting of lead and bismuth, said metal being added in the form of suitable salts up to 3 per cent 01' the total mixture.

4. A luminescent substance highly responsive to radiation having a wave lengthoi 2537 Angstrom units and highly emissive in the range or approximately 3000-t0 4800 Angstrom units, said substance being a silicate of a metal of the group consisting of aluminum, beryllium and magnesium actlvated by an addition of cerium sesquioxide and a metal oi the group consisting 01 lead and bismuth, said metal being added in the form of oxides up to 3 per cent 01' the total mixture.

5. A lubminescent substance highly responsive to. radiation having a wave length of 2537 Angstrom units and highly emissive in the range of approximately 3000 to 4800 Angstrom units, said substance being a silicate of a metal of the group consisting 01' aluminum, beryllium, and magnesium, activated by an addition of cerium sesquioxide, and also containing an addition of up to approximately 50 per cent 01 a compound of the group consisting of the fluorides of calcium, barium and strontium.

GUN'IfHER ASCHERMANN. 

